#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
	double sum = 0;
	for (int i = 1; i <= 100; i++)
	{
		if (i % 2 == 0)
			sum -= 1.0 / i;
		else
			sum += 1.0 / i;
	}
	printf("%f\n", sum);
	return 0;
}